The present invention relates, in general, to process control for controlling the output of an industrial process, and in particular to a new and useful adaptive process control which is made up of individual function blocks assembled to generate one or more tuning parameters, without the use of a computer or corresponding computer software.
The automatic control of various industrial processes, such as those found in chemical, power and heat transfer plants, involves the identification and manipulation of plant parameters and disturbances to produce suitable control signals.
Many adaptive controls require on-line identification of such parameters which means that a digital computer is required. See for example D. E. Seborg and D. G. Fisher "Experience with Experimental Applications of Multivariable Computer Control," ASME Paper 78-WA/DSC-26; and H. Unbehauen, et al "Comparison and Application of DDC Algorithms for a Heat Exchanger", Journal of Automatica, Vol. 12, 1976, pp. 393-402.
As disclosed in G. Schinskey "Process Control Systems", Chapter 6, McGraw-Hill, 1978, some low-level controls which are referred to as selective and adaptive controls, can be implemented by analog control equipment. The function of selective control is to select the variable to be controlled on a multi-variable process having a single feed-back control loop. Adaptive control changes the values of control paramaters as the process parameters (such as flow) vary.
In addition, optimum control values can be found by way of optimum tuning processes for a given operating condition of a process. See, for example, A. A. Rovira, et al., "Tuning Controllers for Set Point Changes,"Instruments and Control Systems, December 1969. In this arrangement, the choice has to be made as to whether optimum control values are to be tuned for a set point change or for various disturbances in the process. Such disturbances include changing values of temperature, flow rate and the like.
Even in single loop controls, computers are being utilized due to the flexibility offered. Accordingly, the use of computers for control of a process have increasingly replaced analog control equipment. See E. B. Dahlin, "Designing and Tuning Digital Controllers", Instruments and Control Systems, June 1968.
Shortcomings of the four mentioned approaches to process control include the expensive use of computers with corresponding software programs and adaptive controls. Shortcomings of the low-level control approaches include a lack of in-depth consideration of the dynamic characteristics, which in-depth consideration is desirable for proper process performance under varying operating conditions. That is, analog controls are not sufficiently accurate or flexible for the calculations necessary to achieve desired performance.